If the wall is non-load bearing you can build it as you please.
You don't need drywall or tile either. Save on paint and drywall mud.
The inspectors I work with check the bones and structure of the house. Each inspector making sure things are safe and sound.
You will find that not conforming to the norm will set you up for a lot of questions and a lot of lost time in extra drawings and rational discussions.
If you want more room to access the pump - put in a mini header but keep things on 16" centers so your 60" cement board and your 14.5" insulation fits the ready made framing.